The invention relates to a continuous casting mold having mold side walls supported on an oscillating lifting table and having a stirrer comprising a magnetic circuit with a yoke at least partly surrounding the mold side walls and the yoke has at least two cores that are directed against mold side walls which are arranged opposite each other.
In continuous casting, the melt is caused to flow into the continuous casting mold from a tundish either directly or through a casting tube. Due to its kinetic energy, the pouring stream exiting from the tundish or exiting from the casting tube, respectively, penetrates deeply into the liquid core of the strand forming in the continuous casting mold. In this process, entrainment of slag particles, casting powder or other impurities may occur, which entrainment leads to inclusions in the strand if these impurities penetrate very far inside, since separation or flowing upward of the slag etc. to the meniscus of the strand can hardly occur any longer.
To enable control of the flow behavior of the pouring stream inside the continuous casting mold, particularly to prevent the pouring stream from penetrating too far into the liquid core of the strand, it is known to provide a stirrer directly at the continuous casting mold, which stirrer or creates causes a magnetic field that slows down the velocity of the pouring stream and, in addition, advantageously divides the pouring stream. The operation of such a stirrer is comparable to that of an electromagnetic brake.
Continuous casting molds with electromagnetic stirrers of the initially described kind are known for example from EP-B -0 265 796, EP-A - 0 401 504, EP-B - 0 286 935 and WO 92/12814. In accordance with the prior art, the yokes, which constitute a considerable mass, are arranged stationarily to avoid loading the oscillation drives for the mold side walls with these masses. Mostly, the iron cores likewise have been stationarily arranged, in order to avoid loading the oscillation drives with these masses as well. The yoke that has to be additionally provided at the continuous casting mold not only causes substantial structural expenditures (in that additional neon in the very confined space of the continuous casting mold room has to be made for this yoke), but also renders mold construction more expensive due to the additional expenditures incurred for the material.
To enable perfect oscillation of the mold side walls relative to the stationarily arranged stirrer, an air gap is provided between each of the cores of the stirrer and the mold side walls. As a consequence, considerable magnetic forces arise during the operation of the stirrer, which act on the mold side walls and cause a deformation of the mold side walls in the direction toward the core or the yoke. With continuous casting molds for casting a strand having a slab cross section, the molds are constructed as plate molds having broad side walls and narrow side walls clamped between the broad side walls. The narrow side walls either will be clamped only to an unsatisfactory degree by the broad side walls which are acted upon by the magnetic forces, or the forces acting from the stirrer will have to be compensated for by the clamping forces. In the latter case, excessive clamping forces exist between the broad and n arrow side walls when the stirrer is de-engized or put out of action.
It is internally known to rigidly arrange the iron core in the broad side walls of a mold provided for casting a strand having a slab cross section, and the yoke in this case is arranged at a certain distance from the iron cores which are integrated into the broad side walls of the continuous casting mold. Here too, deformations result during the operation of the stirrer, due to the air gap between yoke and core and due to the forces drawing the broad side walls toward the yoke.
A further disadvantage of this construction has to be seen in that for each mold there has to be provided a separate stirrer, which also has to be exchanged whenever the mold side walls are exchanged (for instance in order to change the strand format, etc.).
A continuous casting mold of the initially described kind in which the lifting table that imparts an oscillating movement to the mold side walls is constructed as a yoke, is known from WO-A -94/16844. However, this document does not disclose how the cores are arranged.